Global login page for all domains

Is there a way to have a global login page? For instance, instead of having the customer always go to www.theirdomain.com/cpanel, they could go to a page on my site, enter their domain and password and have it open up in the same or new window?

Description: This script allows you to use a login box on your web page, to login to an htaccess protected directory, instead of the usual htaccess popup. It can be used for any htaccess protected directory. May also be used as a CPanel login box. No database required, only PHP4.